In addition to dynamin, other dynamin family members have been implicated in a variety of fundamental cellular processes, including mitochondrial fission and fusion, anti-viral activity, plant cell plate formation and chloroplast biogenesis. Among these proteins, self-assembly and oligomerization into ordered structures is a common characteristic and, for the majority, is essential for their function. Although there is a wealth of information regarding dynamin, little is known about the structural properties of dynamin-related proteins. In recent years, we have examined two dynamin family members, one involved in mitochondria fission (Dnm1) and the other involved in mitochondrial fusion, Opa1. We are testing the hypothesis that dynamin family members share a common mechanism of action. Our work provides clear evidence that dynamin related proteins have similar assembly and GTPase properties. However, structural constraints must still allow for their widely diverse biological functions. The dynamin family of proteins consists of unique GTPases involved in membrane fission and fusion events throughout the cell. Our goal is to understand the dynamic structural properties of these proteins and correlate them with their diverse cellular functions. Dynamin is essential for endocytosis and vesiculation events in the cell. Additional dynamin family members have been implicated in a variety of fundamental cellular processes, including mitochondrial fission and fusion, anti-viral activity, cell plate formation and chloroplast biogenesis. Among these proteins, self-assembly and oligomerization into ordered structures is a common characteristic and, for the majority, is essential for their function. Although there is a wealth of information regarding dynamin, little is known about the structural properties of dynamin-related proteins. To determine if a common mechanism of action exists among the dynamin family members, we examined the structure and function of Dnm1, a yeast dynamin family member involved in mitochondria fission and Opa1, a human dynamin involved in mitochondria fusion. Previously, in collaboration with Dr. David Chan from Cal Tech, we examined the structure of OPA1 by negative stain and cryo electron microscopy. Mutations in OPA1 (autosomal dominant optic atrophy) can lead to an inherited neuropathy of the retinal ganglion cells. In the cell, OPA1 has been shown to be essential for the fusion of the inner mitochondrial membranes, but its mechanism of action remains poorly understood. Addition of OPA1 to liposomes containing cardiolipin results in enhanced GTP hydrolysis rate and promotes OPA1 to self-assemble into helical arrays around the lipid, forming protein-lipid tubes. Currently we are solving the structure of OPA1 by helical and single particle image processing methods. The conformational state of OPA1 during GTP hydrolysis is also being examined.